When pipe is bent, in order that it will remain of uniform circular cross section over the length of the bend, it is necessary to support the pipe wall at the interior of the pipe. If pipe is bent without being internally supported, the pipe wall at the outside of the bend will not stretch as it should, and the pipe crimps at the inside of the bend. In addition, the pipe becomes noncircular, of flattened oval shape. A number of internal pipe bending mandrels are provided by the art, but none of these are completely satisfactory in use.
According to the invention, an internal pipe bending mandrel is provided which fully supports the pipe in the plane of the bend, so that the pipe will remain uniformly circular over the entire length of the bend. A plurality of jack assemblies are provided spaced along the length of the apparatus. Each jack assembly includes plural jack devices and the jacking action is uniform transverse to the plane of the bend. When the apparatus is used, all of the jack devices operate simultaneously and uniformly to provide uniform support of the pipe walls. The action of the mandrel is sufficiently strong that the pipe may be made to be of slightly oblong shape along the plane of the bend if such is desired.
A principal object of the invention is to provide a satisfactory internal pipe bending mandrel. Another object of the invention is to provide such a mandrel which is relatively simple, easily repaired, easily maintained, and which is durable in use. A still further object of the invention is to provide such a mandrel which provides uniform support of the pipe walls during bending. A further object of the invention is to provide a pipe bending mandrel which is relatively economical in manufacture and use, and which is entirely reliable.
Other objects and advantages of the apparatus afforded by the invention will appear from the following detailed description of a preferred embodiment, and from the accompanying drawings, to which reference will be made during the description.